1. Field of the Invention
The present invention relates to an angular velocity sensor which detects angular velocity acting on an object, more particularly to an angular velocity sensor of an electrostatic capacitance detection type which detects the angular velocity acting on the object based on a change of an electrostatic capacitance.
2. Description of the Related Art
In wide fields including a camera-shake correction device of a video camera, an air back device for a vehicle and a posture control device of a robot, a mechanical dynamic quantity sensor such as an acceleration sensor or an angular velocity sensor is used.
As such a mechanical dynamic quantity sensor, there has been known an electrostatic-capacitance-detection-type sensor which detects the displacement of a mass based on a change of electrostatic capacitance between an electrode mounted on a mass (a mass body) which constitutes a movable body and a fixed electrode, and detects a mechanical dynamic quantity based on the displacement of the mass.
In such an electrostatic-capacitance-detection-type mechanical dynamic quantity sensor, to detect the change of the electrostatic capacitance between the electrodes, a C/V (electrostatic capacitance/voltage) conversion device which converts the electrostatic capacitance to a voltage corresponding to the electrostatic capacitance is used.
The C/V conversion device includes, for properly detecting a minute change of the electrostatic capacitance, an amplifier which amplifies amplitude of a signal for every axis or for every electrostatic capacitance element for detecting a mechanical dynamic quantity acting on the object.
The number of amplifiers for such signals is increased along with the increase of the number of detection axis of the mechanical dynamic quantities and hence, there is observed a tendency that a circuit becomes complicated and large-sized with respect to a multiple-axis detection type sensor.
Accordingly, conventionally, as described in the following patent document, a technique which reduces the number of operational amplifiers in the C/V conversion device has been proposed.
Patent Document 1: JP-A-2005-315824
Patent document 1 proposes the technique which measures the electrostatic capacitances of a plurality of different electrostatic capacitance elements using one operational amplifier.
To be more specific, carrier signals whose phases are shifted from each other by 90° are applied to the electrostatic capacitance elements which are objects to be measured, and all outputs of the electrostatic capacitance element are inputted to the operational amplifier. Then, by performing phase division processing with respect to the output signals of the operational amplifier using a synchronous detection circuit, detection signals of the electrostatic capacitances of the respective electrostatic capacitance elements are separated from each other.
Here, the above-mentioned technique which separates the signals based on the phase division processing can only separate two kinds of signals and hence, when it is necessary to simultaneously measure (detect) the electrostatic capacitances of three or more electrostatic capacitance elements, frequency separation processing which changes the frequencies of the applied carrier waves is used to cope with such a measurement.
However, when the electrostatic capacitances of three or more electrostatic capacitance elements are simultaneously measured (detected) using the technique described in patent document 1, for example, when the displacement of a mass in three axes consisting of an x axis and a y axis which constitute detection axes and a z axis which constitutes an oscillation axis is detected as in the case of a two-axis angular velocity sensor, it is necessary to provide a plurality of signal sources which differ in frequency.
In this manner, it is difficult to prevent the circuit from becoming complicated and large-sized with the provision of the plurality of signal sources.